In 1978, the company Paul Wurth S. A. proposed such a loading device, which is described in detail in U.S. Pat. No. 4,273,492. The suspension rotor in this device is fitted with a lower protective screen which surrounds the chute feed channel and protects the drive means mounted in the housing against the radiant heat from the inside of the shaft furnace in particular. To this end, the lower screen contains a cooling circuit which is supplied with liquid coolant via a rotating annular connection around the chute feed channel. This rotating connection comprises a rotating ring and a fixed ring. The rotating ring is an extension of the suspension rotor and forms an integral part of it, extending beyond of the housing. The fixed ring is fastened to the housing and the rotating ring has a clearance around the fixed ring. Two cylindrical roller bearings are fitted, designed to centre the rotating ring in the fixed ring. The fixed ring comprises two annular grooves one above the other, facing the external cylindrical surface of the rotating ring. Ports in the external cylindrical surface of the rotating ring facing the two grooves define the connection passages of the cooling circuit. Watertight fittings mounted along both sides of each groove abut the external cylindrical surface of the rotating ring to ensure that there are no leaks between the rotating ring and the fixed ring. In practice, it has emerged that a rotating joint of this kind is largely unsuitable for a shaft furnace. Indeed, to avoid cooling water leaking into the housing, it is essential to ensure that there are no leaks between the rotating ring and the fixed ring; but, in a shaft furnace, the effectiveness of the watertight fittings deteriorates rapidly, being as they are in contact with a very hot moving ring, which does nothing for their life cycle. Given the variable thermal expansion which occurs, the radial clearance between the rotating ring and the fixed ring varies considerably, which also has an adverse effect on the life cycle of the watertight fittings, and may even cause the rotating joint to seize up and be completely destroyed. It should also be noted that the life cycle of the rotating joint is affected by violent shocks which the suspension rotor with the chute inevitably absorbs. Lastly, it should be noted that such a large diameter rotating joint, fitted with watertight fittings, involves considerable levels of friction, which considerably increases the power required to start the chute moving. In conclusion, it emerges that a rotating joint of the type described in U.S. Pat. No. 4,273,492 has too many disadvantages to be a viable solution to feeding a cooling circuit mounted on a feed device for a rotary furnace.
To avoid all these disadvantages, as early as the company Paul Wurth S. A. proposed a cooling device for a loading system for a blast furnace without any watertight fittings. This cooling device, which is described in detail in U.S. Pat. No. 4,526,536, has been installed in numerous installations for loading blast furnaces throughout the world. It is characterised by an upper annular tank, which is mounted on an upper sleeve of the suspension rotor and which is fed with cooling water by gravity. A cooling water circuit is incorporated in the housing, and comprises one or more ports above the upper annular tank enabling cooling water to flow by gravity into the upper annular tank, which rotates together with the suspension rotor. The upper cooling tank is connected to a number of cooling coils installed on the suspension rotor. These coils have outlet pipes discharging into a lower annular tank which is fixed and cannot rotate, as it is mounted on the bottom of the housing. The water therefore flows by gravity from a fixed non-rotating supply into the upper annular tank of the suspension rotor, then passes under the influence of gravity into the annular housing tank and is then discharged from the housing. Water gauges in the two annular reservoirs enable the circulation of cooling water to be monitored. In the upper annular tank, the level is adjusted such that it remains between a minimum level and a maximum level at all times. If the level falls to the minimum level, the supply to the annular tank is increased to ensure the necessary supply to the coils. If the level rises to the maximum level, the supply to the annular tank is reduced to avoid the annular tank overflowing.
The first disadvantage of the 1982 cooling device is that the pressure available to move the cooling water through the cooling circuits is essentially governed by the difference in height between the upper tank and lower collecting tank. The suspension rotor must therefore be fitted with low-loss cooling circuits, which is a considerable disadvantage in terms of space occupied and/or cooling efficiency. In particular, there is a risk of local overheating due to the slow circulation speed of the cooling water in the cooling coils. A second disadvantage of the cooling device of 1982 is that the gases from the blast furnace come into contact with the cooling water already in the upper annular tank. As these blast furnace gases carry considerable quantities of dust, this dust inevitably passes into the cooling water. This dust forms sludge in the upper annular tank, which passes through the cooling coils and may block them up. The blast furnace gases also turn the cooling water acid, which tends to corrode the cooling circuits.
To create cooling circuits of higher capacity, it has been proposed, in patent application DE 3342572, to fit these circuits with an auxiliary pump mounted on the suspension rotor. This auxiliary pump is driven by a mechanism which converts the rotation of the suspension rotor into rotation of a drive shaft for the pump. It follows that the auxiliary pump only works when the rotor is rotating; and furthermore, such an auxiliary pump is rather sensitive to the sludge which passes through the cooling coils.
Patent application WO 99/28510 presents a method for cooling a loading device of the type described above, which is fitted with a rotating connection. Contrary to the doctrine of the state of the art, no attempt is made to ensure that the rotating connection is totally watertight, as required in U.S. Pat. No. 4,273,492, for example, nor to avoid leaks outside the rotating connection by a system of level controls, as specified in U.S. Pat. No. 4,526,536. Instead, it is proposed to provide a supply of liquid coolant to the rotating connection in such a way that a leakage flow passes into an annular separation slit between the rotating and fixed sections of the connection to form a liquid watertight fitting which prevents dust penetrating into the rotating connection. This leakage flow is then collected and drained off out of the housing, without passing through the cooling circuit. The result of this is that dust sludge no longer passes through the cooling circuit, and so does not risk clogging it up.
Patent application WO 99/28510 proposes a number of embodiments of the rotating annular connection. In a first embodiment, the fixed section is an annular block which is adjusted with clearance in an annular channel of the suspension rotor, such as to be separated from each of the cylindrical walls of that channel by an narrow annular radial slot. To reduce the leaks via these two annular radial slots, patent application WO 99/28510 proposes to provide each annular slot with one or more lipped watertight fittings or to design each annular slot as a labyrinth watertight fitting. One drawback with this method is that the annular channel in the suspension rotor has to be machined with great precision, and is therefore very expensive. The annular block must also be fitted very precisely in the annular channel of the suspension rotor. This also means that this method is highly prone to centring errors of the rotation of the suspension rotor, and to violent shocks absorbed by the suspension rotor. Another drawback is that the complete suspension rotor has to be removed to repair a damaged annular channel. In an alternative embodiment, the fixed section of the rotating joint consists of a fixed rotary ring, which rests axially, via two watertight fittings, on a ring mounted in an annular channel in the suspension rotor. This fixed rotary ring can slide vertically, such that it can be pressed against the ring mounted in the annular channel of the suspension rotor. This method is relatively vulnerable to variation in the plane of rotation of the suspension rotor. Such variations in the plane of rotation of the suspension rotor are hard to avoid, since the loads on the bearing ring supporting the suspension rotor in the housing are not generally symmetrical with respect to the axis of that rotation, and vary with the angular position of the loading chute.
In conclusion, more than twenty years after the date on which U.S. Pat. No. 4,273,492 was lodged, there is still no satisfactory solution to supplying rotary equipment in a loading device for a shaft furnace with a pressurised liquid coolant.